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WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES
Kannan et al.
World Journal of Pharmacy and Pharmaceutical Sciences
SJIF Impact Factor 2.786
Volume 3, Issue 10, 713-732.
Research Article
ISSN 2278 – 4357
SPECTROSCOPIC ANALYSIS OF CRYSTAL VIOLET DYE
REMOVAL BY SIDA RHOMBIFOLIA: KINETIC, EQUILIBRIUM,
THERMODYNAMIC STUDIES
N.P.Krishnan1, M. Ilayaraja2, R.Karthik2, R. Sayee Kannan2*
1
Department of Chemistry, K.L.N College of Engineering, Pottapalayam-630611, Tamil
Nadu, India.
2
PG Research & Department of Chemistry, Thiagarajar college, Madurai-625009,Tamil
Nadu, India.
Article Received on
21 July 2014,
Revised on 14 August 2014,
Accepted on 05 September
2014
ABSTRACT
The kinetics, adsorption isotherms, thermodynamics and spectroscopic
analysis of the removal of the crystal violet dye by adsorption onto
Sida Rhombifolia were studied. The surface area of Sida Rhombifolia
activated carbon (SRAC) was found to be 18.14 m2/g. Batch
*Correspondence for
adsorption experiments were conducted using dye solution and the
Author
effects of initial dye concentration and contact time, adsorbent dose
Dr. R.Sayee Kannan
P.G & Research Department
and temperature were investigated. The Sida Rhombifolia adsorbent
of Chemistry, Thiagarajar
was charactrerized using FTIR, SEM with EDAX, BET and XRD. The
College, Madurai,
equilibrium adsorption data fitted very well with the Langmuir ,
Tamilnadu, India
Temkin and D-R isotherm model. The kinetic process followed the
pseudo second order kinetic model Positive ∆Ho and negative ∆Go
were indicative of the endothermic and spontaneous nature respectively of Crystal violet
removal by adsorption onto Sida Rhombifolia.
Keywords: Crystal violet, Sida rhombifolia, Langmuir, kinetic, adsorption.
INTRODUCTION
Recently, environmental contaminations by synthetic dyes have become a serious problem
due to their negative ecotoxicological effects and bioaccumulation in wildlife. Most of these
dyes are toxic, mutagenic, and carcinogenic. They are extensively used in industries such as
textile, paint, acrylic, cosmetics, leather and pharmaceutical, which generate a considerable
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amount of colored wastewater. It is difficult to degrade dyes because they have complex
structure and most of them contain aromatic rings, which make them mutagenic and
carcinogenic
[1–3]
. The color in water bodies reduces light penetration and photosynthesis,
therefore, affects the aquatic life. Moreover, dyes are one of esthetic pollution and
eutrophication sources. So it is highly desirable to remove dyes from water/wastewater before
discharging.
Various techniques such as chemical precipitation [4], coagulation [5], biochemical degradation
[6]
, solvent extraction
[7]
, sonochemical degradation
[8]
, photo catalytic degradation
[9]
,
micellar enhanced ultra filtration [10], electrochemical degradation [11], ozone oxidation [12-13],
ion exchange
[14–16]
and adsorption
[17–20]
etc., are used to remove dyes from wastewater.
Among them, adsorption has been recognized as a reliable alternative due to its ease of
operation, simplicity of design, high efficiency, insensitivity of toxic substances and
comparable low cost of application.
In as much as cost of these methods is quite high, adsorption has a superior for the treatment
of wastewaters compared to the above mentioned processes
[21]
. There is a need to produce
low cost and effective carbons that can be applied to water pollution control. A wide variety
of low cost materials has been exploited for the removal of dyes from aqueous solutions,
including lemon peel
[22]
, sugarcane dust
[23]
, orange peel
[24]
, ground nut shell
[25]
, coconut
tree [26], etc.
In the present study, SRAC prepared from waste kurumthotti (Sida Rhombifolia) by chemical
activation with con.H2SO4 was used as an adsorbent to removal of basic Crystal violet dye
(CV) from aqueous solution. The objective of the work is to examine the applicability of the
prepared activated carbon in removing basic dyes from aqueous solutions. The effects of
different parameters including initial concentration of dye solution and contact time,
adsorbent dose and temperature were investigated. The adsorption kinetics, isotherms and
thermodynamic properties were also explored.
MATERIALS AND METHODS
Dye Solution Preparation
The dye crystal violet [C.I name = Basic violet 4, chemical formula weight = 407.9, λmax617nm] is supplied by S.D fine Chemicals, Mumbai, India was used as such without further
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purification. An accurately weighed quantity of dye was dissolved in double distilled water to
prepare the stock solutions.
Adsorbent
Kurumthotti (Sida Rhombifolia) was used as an adsorbent, was collectively obtained from
Nedunkulam, Sivagangai (India) washed with tap water and finally with double distilled
water to remove the suspended impurities, dust, and soil and then dried in oven. About 500g
of powdered kurumthotti was mixed with 100ml of con. sulfuric acid and kept at room
temperature for 24h. and was then dried in a hot air oven at 80˚C. The dried material was
washed with distilled water for removing excess of acid. Finally charcoal was dried in 110˚C
for 12 h to remove moisture and kept in an airtight bottle [27].
Adsorption Experiments
Batch mode adsorption studies were carried out by adding certain amount of adsorbent and
50ml of dye solutions of certain concentrations, dose, contact time and temperatures in a
thermo stated water bath shaker with a shaking of 200 rpm. The samples were withdrawn
from the shaker at predetermined time intervals and solutions were separated from the
adsorbent by centrifugation at 4000 rpm for 5 min. To determine the residual dye
concentration, the absorbance of the supernatant solution was measured before and after
treatment with double beam spectrophotometer (JASCO V530 Spectrophotometer).
Experiments were carried out twice and the concentrations given were average values. The
initial dye concentrations in the test solution and the contact time were changed to investigate
their effect on the adsorption kinetics. The pH of the dye solution was adjusted by using
NaOH or HCl solution. The adsorption studies were carried out at different temperatures
(308K, 318K and 328K). This is used to determine the effect of temperature on the
thermodynamic parameters.
The amount of adsorption in batch experiments, q (mg g -1) (1) and adsorption efficiency (2)
were calculated as follows
q
= (Co - Ce) / m
×V
(1)
Efficiency (%) = (Co -Ce) / Co ×100
(2)
Where, Co
is the initial concentration (mg.L-1)
Ce
is the equilibrium concentration (mg.L -1)
V
is the volume of solution (mL)
M
is the mass of adsorbent (g)
q
is the amount of adsorbed (mg/g)
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Surface Characteristic of the Adsorbent
Surface area and porous size distribution of SRAC sample were measured by nitrogen
adsorption analysis (Quantachrome V5.02). Crystal structure of sample was determined by
performing X-ray diffraction (XRD) on SHIMADZU 6000 X-ray diffraction spectrometer.
Surface morphologies were examined by a scanning electron microscope (SEM, JEOL (JSM
6390) with the working distance of 9.9 mm and an accelerating voltage of 30 keV. The SEM
was equipped with an energy dispersion spectrometer (EDS) and it was used to perform the
analysis of chemical constituents of the adsorbent. Infrared absorption spectroscopy (IR)
spectra were measured at room temperature on a Fourier transform infrared (FTIR)
spectroscopy (8400s SHIMADZU spectrometer) using the KBr pellet technique.
RESULTS AND DISCUSSION
Characterization of the Adsorbent
BET
The surface area of SRAC was found to be 18.14 m2/g. Total pore volume is 10.00 cm3/g and
pore size is 408.3 . SRAC has a relatively promising surface area although it was obtained
from kurumthotti only by carbonization process as shown in “Fig. 1”,
Fig. 1. Adsorption-desorption isotherms of nitrogen at 77 K on SRAC
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FTIR
FTIR spectra of the raw material, SRAC, SRAC-CV, MAC-CR were shown in “Fig. 2”,
FTIR data of raw material showed that characteristic band at 3285.1, 1624.5, 1238.0 and
1032.5 cm-1 correspond to the free OH, aliphatic, C=C stretching and C-O-C stretching
vibrations respectively “Fig. 2”,(a).
The FTIR spectrum of chemical activated carbon (SRAC) was exhibited in “Fig. 2”, (b) After
modification Free OH group disappeared. The new band appeared at 1601.6 cm-1 and 1013.7
was assigned to C=O stretching vibration and C-O-C vibrations respectively. The band
observed at 755.6 cm-1 was due to the CH=CH stretching vibrations.
“Fig. 2”, (c) indicated that mostly the bonded C=O stretching, C-H bending vibrations, C-OC vibrations and –CH=CH- were involved in CV adsorption. A new band was observed in the
after adsorption at1438.44. There were clear band shifts and intensity decrease in “Fig. 2”, (c)
These findings suggest that there is attachment of CV on the SRAC.
Fig. 2. FTIR spectra of: (a) Raw material (b) SRAC (c) SRAC-CV
XRD
The XRD patterns as shown in “Fig. 3”, were performed to analyze the crystalline nature.
The characteristic 20˚-30˚ peaks of SRAC were discernible in carbon, the diffraction
spectrum of SRAC did not show any obvious crystalline peak at the scan range 10-60˚
thereby indicating the amorphous phase of SRAC.
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Fig. 3. XRD pattern of SRAC
SEM
“Fig. 4”, showed the SEMs of SRAC and SRAC adsorbed CV dye. The particles (“Fig. 2”,
(a) appeared obviously diverse. Clearly, there were particle fragments and irregular structure
on the surface. Such cracks and irregularities are beneficial for the dye removal to diffuse to
the inner adsorption sites located in the interior portion of the adsorbent. “Fig. 2”, (b) showed
micrographs of the SRAC surface after adsorbed CV dye, which is covered with some small
particulates on the surface, suggesting CV dye has been adsorbed.
A
B
Fig. 4. The SEM images of (a) SRAC (b) SRAC-CV
EDX
Further confirmation of the adsorption of CV on SRAC carbon was done by energy
dispersive X-ray analysis (EDX). ). “Fig. 5”,(a) for the unloaded SRAC showed four
characteristic signals for C, O, S and Ca composition as 82.93%, 16.11%, 0.78% and 0.18%
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respectively. The EDS spectrum “Fig. 5”, (b) of after adsorption of SRAC-CV presented the
same element but C atomic percentage was decreased from 82.93 to 61.98% and oxygen
percentage was increased from 16.11 to 36.76%. The Ca atom also increased from 0.18 to
0.91%. The S atom also decreased from 0.78 to 0.35%.
It provided an evidence for
CV adsorption onto SRAC surface.
18
a
cps/eV
b
16
14
12
10
S
8
Ca
C O
S
Ca
6
4
2
0
1
2
3
4
keV
5
6
7
Fig. 5. Energy dispersive spectra of (a) SRAC (b) SRAC-CV
UV-Visible
“Fig. 6”, (a) indicates that before the adsorption of CV dye a high intensity peak is observed
but after the adsorption of CV dye onto SRAC the peak intensity decreased due to dye
adsorption shown in “Fig. 6”,(b)
Fig.6. UV-Vis spectra of (a) Before adsorption of CV dye (b) After adsorption of CV dye
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Table.1.Effect of dye concentrations
Time
(min)
10
20
30
40
50
Crystal violet dye concentrations (ppm)
Adsorption Efficiency (%)
Amount of adsorbed (q) mg/g
50
60
70
80
90
50
60
70
80
90
59.2 54.8 12.2 13.6 5.0
320 510 110 130
50
68.5 67.7 20.0 18.9 9.0
370 630 180 180
90
81.4 73.1 27.7 27.3 17.1 440 680 250 260
170
83.3 77.4 30.0 30.5 22.2 450 720 270 290
220
87.0 82.7 36.6 35.7 26.2 470 770 330 340
260
Effect of Initial Dye Concentrations and Time
The effect of initial CV concentration on the percentage removal of the dye is shown in
Table.1. The initial CV concentration was varied from 50 to 90 mg/L. A rapid initial
adsorption of CV took place within the first 20 min, after which the adsorption slowed down
and then almost reached at 50 min. The percentage of CV removal evidently decreased with
increasing initial dye concentration. The percentage of removal was 87 % for 50 mg/L initial
concentration and only 26.2% for 90 mg/L after 50 min of adsorption. This was caused by an
increase in the mass gradient pressure between the solution and adsorbent. The gradient acted
as the force that drove the transfer of the dye molecules from the bulk solution to the particle
surface.
Effect of Adsorbent Mass
The effect of adsorbent dosage varied from 0.010 to 0.050 g/L on the percentage removal of
50 mg/L CV solution is shown in Table.2. The percentage of removal of CV from the
solution increased from 35.10% to 70.21% as the adsorbent dosage increased from 0.010 to
0.050 g/L. This result is expected because of the increased adsorbent surface area and
availability of more adsorption sites caused by increasing adsorbent dosage.
Table.2.Effect of Adsorbent mass (g)
Time
(min)
10
20
30
40
50
Adsorbent mass (g)
Amount of adsorbed (q) mg/g
0.010 0.020 0.030 0.040 0.050 0.010 0.020 0.030
0.040
0.050
6.3
8.5
29.7
35.1
54.2
60
80
280
330
510
15.9
18.0
35.1
39.3
58.5
150
170
330
370
550
21.2
26.5
37.2
44.6
61.7
200
250
350
420
580
27.6
38.2
43.6
48.9
65.9
260
360
410
460
620
35.1
44.6
50.0
55.3
70.2
330
420
470
520
660
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Adsorption Isotherms: The experimental data collected at 298 K and the initial
concentration of 50 mg/L were fitted on the standard models used in waste water treatment
application: Langmuir, Freundlich, Temkin, Jovanoic and D-R isotherm respectively.
A Langmuir isotherm assumes monolayer onto a surface containing a finite number of
adsorption with no transmigration of the adsorbate in the plane of the surface. The linear form
of the Langmuir isotherm equation is given as
Ce
=
1
Ce
+
qe
KL× qm
(3)
qm
Where Ce is the equilibrium concentration of the adsorbate (mg/L), q e is the amount of
adsorbate adsorbed per unit mass of adsorbent (mg/g), KL the Langmuir adsorption constant
(L/mg), and qm is the theoretical maximum adsorption capacity (mg/g). Plotting Ce against
Ce/qe “Fig. 7”, gives a straight line with slope and intercept equal to qe and KL, respectively.
Fig. 7. Langmuir isotherm plots for the adsorption of CV onto SRAC
In order to determine if the adsorption process is favorable or unfavorable, a dimensionless
constant separation factor or equilibrium parameter RL is defined according to the following
equation [28]
RL = 1/1+ KL Co
(4)
Where, KL is the Langmuir isotherm constant (L/mg) and C o is the initial dye concentration
(mg/L). The RL value indicates the type of the isotherm to be either unfavorable (R L>1),
linear (RL=1), favorable (0<RL<1), irreversible (RL=0).
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The Freundlich isotherm, on the other hand, assumes heterogeneous surface energies, in
which the energy term in the Langmuir equation varies as a function of the surface coverage
[29]
. The well known logarithmic form of the Freundlich isotherm is given by the following
equation
log qe = log KF + 1/n log Ce
(5)
where, Ce is the equilibrium concentration of the adsorbate (mg/L), q e is the amount of
adsorbate adsorbed per unit mass of adsorbent (mg/g), KF and n are Freundlich constants with
n giving an indication of how favorable the adsorption process is and K F (mg/g) is the
adsorption capacity of the adsorbent. Plotting ln q e against ln Ce gives a straight line with
slope and intercept equal to 1/n and
ln KF, respectively. The Freundlich constant 1/n is
smaller than 1, indicates a more heterogeneous surface whereas a value closer to or equal to
one indicates that the adsorbent has relatively more homogeneous binding sites.
In order to determine the type of adsorption, D-R isotherm has also been tested for the
sorption of CV onto SRAC. The D-R equation can be defined by the following equation [30].
ln qe = ln qm – βε2
(6)
In this equation, β a constant related to the adsorption energy (mol2/kJ2), qm is a constant that
indicates the sorption degree characterizing the sorbent (mg/g) and ε is the Polanyi potential
shown in Eq.7:
ε = RT ln (1+1/Ce)
(7)
Where, T is the absolute temperature (K) and R is the ideal gas constant (R=8.314 J/mol K).
By plotting ln q e vs ε2, it is possible to determine the value of β from the slope and the value
of qm from the intercept, which is ln qm.
The mean free energy E (kJ/mol) of sorption can be estimated by using β values as expressed
in the following equation [31].
E = 1/ (2β) 1/2
(8)
The magnitude of E may characterize the type of the adsorption as chemical ion exchange
(E=8-16 kJ/mol), or physical adsorption (E<8 kJ/mol). The mean free energy of adsorption
for the present study was found to be CV has 0s KJ/mol. This implies that, the adsorption of
CV dye on SRAC may be considered as physical adsorption process.
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The linearized form of Temkin isotherm is given as
qe = B1 ln KT + B1 ln Ce
(9)
Temkin isotherm contains a factor that explicitly takes into account adsorbing species and
adsorbent interactions. This isotherm assumes that (i) the heat of adsorption of all the
molecules in the layer decreases linearly with coverage due to adsorbent-adsorbate
interactions, and that (ii) the adsorption is characterized by uniform distribution of binding
energies, up to some maximum binding energy
[32]
. A plot of q e versus ln Ce enables the
determination of the isotherm constants B1 and KT from the slope and the intercept,
respectively. As shown in Fig 8, KT is the equilibrium binding constant (L/mol)
corresponding to the maximum binding energy and constant B1 is related to the heat of
adsorption.
Fig. 8. Temkin isotherm plots for the adsorption of CV onto SRAC
The Jovanoic isotherm
[33]
, which is based on the same assumptions of the Langmuir
isotherm, also considers the possibility of some mechanical contacts between the adsorbing
and desorbing molecules on the homogeneous surface and can be represented in a linear form
as follows
ln qe = ln qm + KJ Ce
(10)
where, qm is the maximum amount adsorbed (in mg/g) and KJ (in L/mg) is the constant
related to the energy of adsorption. The q m and KJ can be calculated from the intercept and
slope of the linear plot of ln q e against Ce “Fig. 9”,
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Fig. 9. Jovanoic isotherm plots for the adsorption of CV onto SRAC
The R2, qm, KL, RL, R2 (correlation coefficient for Langmuir isotherm), KF, n, R2 (correlation
coefficient for Freundlich isotherm), B1, KT, R2 (correlation coefficient for Temkin isotherm),
β, qm, E, R2 (correlation coefficient for D-R isotherm), R2, KJ, qm (correlation coefficient for
Jovanoic isotherm), are given in Table 4. The data of Table 3 indicate that the Langmuir,
Jovanoic and Temkin isotherms are the most appropriate for adsorption of CV on SRAC.
Table.3. Different adsorption isotherm model parameters for the adsorption of CV on
SRAC.
Isotherms
Langmuir
Freundlich
Temkin
Jovanoic
R2
qm (mg/g)×102
KL (l/mg) ×102
RL
R2
n
KF ×10-3
R2
B1
KT
R2
qm
KJ
R2
qm (mg/g) ×105
D-R
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Crystal violet dye Concentrations (mg/L)
50
60
70
80
90
Constants
β
E (kJ/mol)
0.991
2.79
29.85
0.060
0.985
4.18
11.52
0.085
0.909
4.07
1.90
0.382
0.938
4.73
1.83
0.371
0.549
5.49
1.04
0.493
0.968
2.985
195.8
0.981
131.6
129.3
0.997
6.338
2.559
0.953
2.352
797.9
0.976
269.4
292.7
0.976
2.340
3.621
0.956
0.298
10.25
0.997
675.6
44.8
0.997
1.395
1.476
0.972
0.309
19.86
0.998
711.7
7.75
0.998
1.343
1.402
0.946
0.158
5.11
0.998
831.7
1.38
0.998
1.187
1.201
0.964
21.77
-
-
-
-
-
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Kinetic Studies
Kinetic models have been proposed to determine the mechanism of the adsorption process
which provides useful data to improve the efficiency of the adsorption and feasibility of
process scale-up. The rate constants were calculated by using pseudo-first-order and pseudosecond-order kinetic models and the rate controlling step was determined by intra-particle
diffusion model.
Pseudo-First-Order Model
The Lagergren pseudo first-order model is given by the following equation [34].
ln (qe-qt) = ln qe – k1t
(11)
where, qe and qt are the sorption capacities at equilibrium and time„t‟ respectively and k1
represents the rate constant of the pseudo first-order kinetic model. The data obtained for
sorption of CV on activated carbon based on the pseudo first – order kinetic model showed
that the adsorption kinetics were not in good agreement with the pseudo first-order model.
The inapplicability of the Lagergren model to describe the kinetics of CV adsorption was also
reported by Lata et al [35].
Pseudo-Second-Order Model
The linearized form of the pseudo second-order kinetic model is represented as follows:
t
1
=
qt
t
+
k2qe2
(12)
qe
Where, k2 (g/mg/min) is the second-order rate constant of adsorption. The plot of t/qt versus t
shows a linear relationship. Values of k2 and equilibrium adsorption capacity q e were
calculated from the intercept and slope of the plot shown in “Fig. 10”,
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Fig. 10. Pseudo-second-order kinetic plots for adsorption of CV onto SRAC
Intra-Particle Diffusion Model
For a solid-liquid adsorption process, the solute transfer is usually characterized by external
mass transfer or intra-particle diffusion or both. The intra-particle diffusion model proposed
by Weber and Morris
[36]
was used to identify the mechanism involved in the adsorption
process
qt = kidt0.5 + C
(13)
Where, kid (mg/g/min0.5) is the rate constant of the intra-particle diffusion model and C
(mg/g) reflects the boundary layer effect. The kid and C can be determined from the slope and
intercept of the linear plot of qt against t0.5 shown in “Fig. 11”,
Fig. 11. Intra particle diffusion plots for adsorption of CV onto SRAC
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The kinetic model parameters at different initial concentrations were determined. Table 4
summarizes the parameters and coefficients of the pseudo first-order and pseudo secondorder kinetic and intra-particle diffusion model. Among the tested models, the correlation
coefficient (R2) for the pseudo-second-order adsorption model and intraparticle diffusion
model has high value (> 98). These facts suggested that the pseudo-second-order adsorption
mechanism was predominant, and that the overall rate of the CV adsorption process appeared
to be controlled by the chemisorptions process.
Table. 4. Kinetic parameters for the adsorption of CV dye onto SRAC
Co
(mg/L
)
50
60
70
80
90
First-order model
Second-order model
R
qe mg/g
×10-4
k1
min-1
R
0.842
0.888
0.904
0.943
0.933
50.46
154.5
3.176
4.315
0.254
0.007
0.008
0.024
0.022
0.042
0.996
0.997
0.957
0.935
0.241
2
2
qe g/mg
min-1
×10-2
10
10
10
10
10
k2
g/mg/min
7.14
12.5
1.31
1.49
4.73
Intraparticle diffusion
model
kid
C
2
R
g/mg/
mg/g
min1/2
0.955 39.91
198.4
0.979 63.89
323.2
0.986 54.84
62.76
0.985 54.54
49.15
0.979 56.31
140.5
Effect of Temperature and Thermodynamic Data
The effect of temperature on the adsorption of CV on SRAC particles has been studied in the
range of 308-328K, keeping all the other parameters constant at their optimum value, that is
the sorbent mass (0.050g), the target dye concentration (50 mg/L) and the contact time (50
min). The results show that the adsorption of CV dye is favored by an increase in
temperature.
Table.5. Effect of Temperature
308 K 318 K
328 K
71.7
79.3
84.7
Amount of Adsorbed (q) mg/g
308 K 318 K
328 K
660
730
780
The thermodynamic parameters, namely the enthalpy (ΔH˚) and entropy (ΔS˚) associated
with the adsorption process were calculated from the slope and intercept of the linear plot of
ln KL versus 1/T “Fig. 12”, using the following equation
ln KL = ΔS˚ _ ΔH˚
R
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(13)
RT
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Kannan et al.
where, KL is the distribution coefficient. The correlation coefficient for the linear plot was
R2=0.975 for CV dye.
Fig. 12. van’t Hoff plots of ln K L versus 1/T for the adsorption of CV onto SRAC
The Gibbs free energy of specific adsorption (ΔG˚) was calculated using the equation:
ΔG˚ = ΔH˚ – TΔS˚
(14)
The estimated thermodynamic parameters are presented in Table 6. The positive ΔH˚ values
mean a chemical endothermic process. A positive value of ΔS˚ showed a change in biomass
structure during the sorption process, causing an increase in the disorderness of the system
[37]
. The negative value of ΔG˚ at all temperatures indicated the spontaneous nature of the
adsorption of CV dyes on the SRAC adsorbent.
Table.6. Thermodynamic parameters for the adsorption of Crystal violet dye on SRAC
R2
0.999
ΔH˚
J/mol
33.01
ΔS˚
J/mol K
114.8
-ΔG˚(kJ/mol) ×102
308K
23.85
318K
35.58
328K
46.8
CONCLUSION
Sida Rhombifolia activated carbon (SRAC) prepared by chemical activation with H 2SO4 was
an efficient adsorbent with relatively large surface area of 18.14 m2/g and total pore volume
of 10.0 cm3/g.
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Kannan et al.
The present study showed that SRAC could be used as an adsorbent for the removal of crystal
violet dye from aqueous solutions. From batch experiments, the adsorption amount was
highly dependent on operating variables such as initial concentration of dye, contact time,
adsorbent dose and temperature. The equilibrium time was found to be 50min SRAC-CV
system. The optimum adsorbent dose was found to be 0.050 g/L for CV dye. The adsorption
kinetics was investigated using the pseudo-first-order and pseudo-second-order model.
The kinetic studies showed that the adsorption process followed the pseudo-second-order
model. The equilibrium data were better represented by the Langmuir, Temkin and Jovanoic
isotherm. The negative ΔG˚ and the positive ΔH˚ indicated the spontaneous and endothermic
nature of the adsorption.
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